1. Field of the Invention
The present invention relates to a method of manufacturing a bead inductor and a bead inductor produced by such method such that the bead inductor is adapted for use in a noise controlling circuit and other circuits.
2. Description of the Related Art
As a noise-controlling device, especially a device for use with a microprocessor, for example, which is required to pass a large electric current therethrough, an experimental bead inductor has been proposed and tested. Such a bead inductor is an example of an experimental device which has not been publicly disclosed and is formed of a resin material or a rubber material including a powdery magnetic substance such as ferrite powder having a conductor coil embedded therein. In such a bead inductor, a conductor coil is embedded into a resin material or a rubber material via injection molding or other process, to form a molded body which is cut off at both ends thereof to expose both ends of the coil disposed therein. Then, metal caps are connected thereto via conductive resin paste or spot welding so as to define external terminals.
FIGS. 5 and 6 are sectional views illustrating a method for manufacturing the bead inductor. Referring to FIGS. 5 and 6, a metallic mold for injection molding to manufacture the bead inductor includes an upper mold 1 and a lower mold 2. A cavity is formed in the upper mold 1 and defines a space for molding a resin member. In the lower mold 2, a pin 4 is provided so as to be disposed in the cavities 3 when the upper mold 1 and the lower mold 2 are mated with each other. The upper mold 1 has a gate 1a for supplying a melted resin material into the cavity 3.
In order to manufacture a molded body of the bead inductor using the metallic mold shown in FIG. 5, the pin 4 is inserted into a conductor coil, which is formed by winding a metallic wire such as a copper wire coated by a polyester resin, etc., for insulation. Then, the melted resin including a powdery magnetic substance such as ferrite powder is injected into the cavity 3 via the gate 1a. As a result, the outer portion of the conductor coil having the pin 4 inserted therein is molded of the melted resin.
FIG. 6 is a sectional view showing the state of the outside portion of a coil 5 molded in this manner. After the step shown in FIG. 5, the pin 4 is removed and the same resin material used for the outside portion of the coil 5 is injected into the space produced by the removing the pin 4, so as to mold the inside of the coil 5 of the melted resin, so that the coil 5 is embedded in the resin.
Both ends of the molded body obtained in this manner are cut off by a dicing saw or other cuffing instrument, such that the ends of the coil embedded in the resin of the molded body are exposed.
FIG. 7 is a side view showing the molded body after the cutting step described above is performed and FIG. 8 is a plan view thereof. A molded body 7 is formed by embedding the conductor coil 5 into a resin molding 6. On one of the cutting planes 7a of the molded body 7, one end portion 5a of the conductor coil 5 is exposed. On the other of the cutting planes 7b of the molded body 7, the other end portion 5b of the conductor coil 5 is exposed. In a conventional manufacturing method, metallic caps which define external terminals are attached so that the end portions 5a and 5b of the conductor coil 5 are electrically connected thereto via conductive resin paste or spot welding. Solder may be used to attach the metallic cap, and in this case, solder paste, etc., is coated on the end portions of the conductor coil exposed on the end planes of the molded body or on the metallic caps.
In a conventional bead inductor, the conductor coil inside of the molding is electrically connected to the external terminal via conductive resin paste, spot welding, etc., as described above. As a result, there has been a problem of a low degree of reliability in the electrical connection between the conductor coil and the external terminal. That is, it is difficult to secure the spot welding on the ends 5a and 5b of the conductor coil 5 in the respective cutting planes 7a and 7b of the molded body 7, because the surfaces of the ends are flat as shown in FIG. 7, resulting in a low degree of reliability of the electrical connection when the external terminal such as a metal cap is welded thereon. When the external terminals such as the metal caps are bonded onto the ends 5a and 5b of the conductor coil 5 via conductive resin paste, the connecting reliability is also low because of poor adhesive properties.